1. Field of the Invention
The present invention generally relates to a semiconductor device, and more particularly to a semiconductor device improved so that a contact hole can be formed stably. The present invention also relates to a method of manufacturing such a semiconductor device.
2. Description of the Background Art
A conventional method of manufacturing semiconductor devices will now be described together with a disadvantage thereof. Referring to FIG. 20, a LOCOS oxidation film 2 as an element isolating region is provided in a surface of a silicon substrate 1. LOCOS oxidation film 2 is provided for electrically isolating an element region from another element region. An impurity diffusion layer 3 is provided at an active region. A polysilicon interconnection (gate electrode) 4 is provided on LOCOS oxidation film 2. An interlayer insulation film 5 is provided on silicon substrate 1 to cover polysilicon interconnection 4. Provided in interlayer insulating film 5 are a contact hole 6a for exposing a surface of polysilicon interconnection 4 and a contact hole 6b for exposing a surface of impurity diffusion layer 3.
The depth of contact hole 6a is different from that of contact hole 6b. Thus, if an etching condition is set according to contact hole 6b for exposing a surface of impurity diffusion layer 3, a surface of polysilicon interconnection 4 is removed at a portion of contact hole 6a for exposing a surface of polysilicon interconnection 4.
Referring to FIG. 21, contact holes 6a and 6b are internally covered with a barrier metal layer 7 of e.g. Ti/TiN formed by sputtering, and lamp annealing is then applied so that barrier metal layer 7 reacts with silicon substrate 1 or polysilicon interconnection 4. A TiSi.sub.2 layer 8 is thus formed at a surface of polysilicon interconnection 4 and a surface of impurity diffusion layer 3.
Since polysilicon interconnection 4 is removed at a portion of contact hole 6a, the film thickness of polysilicon interconnection 4 must be increased with consideration for the reduction of the film thickness of polysilicon interconnection 4 due to the removal. Accordingly, conventional devices cannot reduce step. Increasing the film thickness of polysilicon interconnection 4 further increases the depth difference between contact holes 6a and 6b.
Referring to FIG. 22, interconnection layer 6a, 6b is formed to obtain a semiconductor device.
Referring to FIG. 23, for a conventional device, when the registration for forming contact hole 6b is displaced and contact hole 6b thus overlaps with element isolating region 2, an end of LOCOS oxide film 2 is etched simultaneously in overetching the interlayer insulating film 5 to expose a surface of silicon substrate 1.
Referring to FIG. 24, forming a conductive layer 9 while a surface of silicon substrate 1 is exposed causes leakage into silicon substrate 1. Thus, the distance between the end of LOCOS oxide film 2 and contact hole 6b cannot be reduced in the conventional device, disadvantageously resulting in preventing microfabrication of the device.